The present invention relates to an improvement in a chlorine hydrate tank for efficiently forming or synthesizing chlorine hydrate and storing the formed chlorine hydrate, as a storage form of chlorine.
In general, chlorine hydrate is a clathrate compound wherein a chlorine molecule is enclosed within 48 water molecules and has a general formula: Cl.sub.2 .multidot.xH.sub.2 O (where x=6 to 8). Chlorine hydrates can be stably stored if kept at temperatures below 9.6.degree. C. and at normal pressure. Thus, chlorine hydrates are good means of storing chlorine. Synthesis of chlorine hydrate is an exothermic reaction (80 cal/g). Thus, in order to form a chlorine hydrate efficiently, the heat of reaction must be quickly removed. In view of this, according to a conventional method, chlorine and chilled water at 9.6.degree. C. or lower are mixed and directly reacted together to form chlorine hydrate. However, it is extremely difficult to obtain efficient absorption of chlorine gas into chilled water. An improvement in the yield of chlorine hydrate is demanded.
In some cased, a small amount of zinc chloride, sodium chloride or potassium chloride is dissolved in chilled water. In such cases, the formed chlorine hydrate is not deposited on a cooling heat exchanger in the chlorine hydrate tank, and thus the operation capacity of the heat exchanger is maintained. The solution temperature is generally kept at 8.degree. C. or lower.
An example of means for storing chlorine will be described with reference to a case of a zinc-chloride battery. FIG. 1 shows a conventional charging mechanism of a zinc-chloride battery. Referring to FIG. 1, chlorine gas generated by a chlorine electrode in a battery 1 is blown into a chlorine hydrate tank 4 by a gas pump 2 through a chlorine gas supply pipe 3. The chlorine gas in the tank 4 reacts with chilled water 6 held therein and chilled by a heat exchanger 5 so as to form chlorine hydrate 7. The nonreacted portion of the chlorine gas is supplied to a nonreacted gas circulation pipe 16 where it is recirculated for further reaction as indicated by the arrow.
Zinc chloride electrolyte held in an electrolyte tank 8 is supplied to the battery 1 and is recirculated therebetween by a pump 9.
FIG. 2 shows an example of a chlorine hydrate tank for mixing chlorine with chilled water to form chlorine hydrate. In this chlorine hydrate tank, chlorine is blown into chilled water 6 in a chlorine hydrate tank 4 through a chlorine gas supply pipe 3. This tank can only provide a very low reaction rate between the chilled water and chlorine gas. Therefore, it has been proposed to use an agitator so that the chilled water is agitated while chlorine is blown into the chilled water. However, it is difficult to agitate the chilled water uniformly at all times and power is required for agitation.
Furthermore, when a large amount of chlorine hydrate 7 is formed, as shown in FIG. 3, the chlorine hydrate has a high specific gravity and therefore precipitates on the bottom of the chlorine hydrate tank 4. The precipitated chlorine hydrate frequently clogs the distal end of the chlorine gas supply pipe 3 thus preventing further synthesis of chlorine hydrate.
Another method which uses a gear pump has also been proposed. According to this method, chlorine and chilled water are drawn into the gear pump through inlet ports thereof and are mixed therein. The pump then delivers the synthesized chlorine hydrate. This method provides a high mixing efficiency and a high yield of chlorine hydrate. However, when the produced chlorine hydrate is drawn into the pump, the interior of the chilling tank is kept at a reduced pressure. This causes decomposition of the chlorine hydrate and thus reduces the overall yield thereof. In order to prevent this, a filter for separating out the chlorine hydrate is required, resulting in a complex structure. In addition, power for driving the pump is required. Since chlorine-containing water is strongly corrosive, only titanium can be used as a material of the pump, rendering an expensive pump necessary.